The need to equalize fluid flow in a given region is well known. The term "fluid" in this instance may refer to air, gas or liquid. One of the most important applications of equalizing flow is in the area of turbine engines to diminish the occurrence of compressor surge and rotating stall.
Gas turbine engines require high performance and high reliability in order to assure that flights can be completed effectively, efficiently and safely. This is especially true in military applications. Air is forced through the inlet or mouth of a turbine engine and from there directed into an axial compressor. As the flow in an axial compressor is reduced or made non-uniform while the compressor or rotational speed is held constant, a point will be reached at which some or all of the engine blades begin to stall and engine instabilities occur. The most violent of these is "surge", which for high speed compressors (as in a turbine engine) can result in periodically reversed flow and mechanical damage. The other result of air being reduced or made non-uniform is rotating stall. "Stall" can result in a region of blocked flow covering half of the circumference of the engine inlet and rotating at half the rotor speed, and may lock the engine.
When a gas turbine engine experiences a compressor "stall" or "surge", the given flight will be effected. In cases of severe surge, the engine or drive train components can fail, causing loss of engine operation. When this happens in flight, the results can be catastrophic. Similarly, a rotating "stall" can lock or freeze an engine resulting in loss of operation. For an in depth discussion of how a turbine engine works, and turbine engine surge and stall, see Emmons, H. W., Pearson, C. E., and Grant, H. P.; "Compressor Surge and Stall Propagation," Transactions of the ASME, May, 1955, p. 455-469; and Greitzer, E. M., "The Stability of Pumping Systems--the 1980 Freeman Scholar Lecture," ASME J. of Fluids Engineering, Jun., 1981, vol. 103, p. 193-242.
Surge and stall have three causes: (1) engine deterioration; (2) aerodynamic distortions (especially at the air inlet); and (3) hot gas injection (from weapon firing). Despite the knowledge of these causes, there has been little success in providing turbine engines with any reliable way of preventing engine surge or stall.
The present invention addresses cause number (2), and teaches a way to create a flow of air into a turbine engine which is uniform in pressure around the circumference of the engine inlet. As air enters an engine inlet, any variations in pressure at different points around the circumference of the inlet create aerodynamic disturbances and mechanical stress, hence inefficiencies in the engine. If the introduced air is non-uniform in pressure, the stress on the blades of the engine will also be non-uniform, because the blades of a turbine engine are rotating and acting on the introduced air. This stress on the engine causes blade shape deformation, which may further deteriorate the engine and cause the engine to run inefficiently. Uniform pressure around a turbine engine inlet will assure that the flow of air into the engine is constant and uniform, and will reduce engine stress while increasing engine efficiency.
Accordingly, an object of the present invention is to provide an apparatus which may cause fluid pressure in one region to equalize with the pressure in another region.
It is a further object of the present invention to provide an apparatus for equalizing the pressure of air around the inlet duct of a turbine engine.
Still another object of the present invention is to provide a method for equalizing the pressure of air around the inlet duct of a turbine engine.
All publications and references cited herein are hereby incorporated into this specification by reference thereto.